This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application entitled DEVICE AND METHOD FOR COMMUNICATING PACKET DATA IN MOBILE COMMUNICATION SYSTEM earlier filed in the Korean Industrial Property Office on Jul. 13, 1998, and there duly assigned Serial No. 98-28237 and also Korean Patent Application Serial No. 1998-29180.
1. Field of the Invention
The present invention relates to a device and method for communicating packet data in a mobile communication system, and more particularly, to a device and method used for rapidly assigning a dedicated channel for packet data service in a CDMA (Code Division Multiple Access) mobile communication system.
2. Description of the Related Art
In CDMA mobile communication systems, the IMT-2000 standard has evolved from the IS-95 standard. IS-95 supports voice service only, whereas IMT-2000 enables high-quality voice service, transmission of moving pictures, and internet browsing.
Data communication in the mobile communication system is characterized by a momentary active state and a long idle state. Accordingly, the next generation of mobile communication systems assign a dedicated channel in a data communication service only at the time when data is transmitted. That is, dedicated traffic and control channels are connected during data transmission and released after a predetermined time when no data is transmitted, due to limited radio resources, base station (BS) capacity, and mobile power consumption. Once the dedicated channels have been released, communication is made via common channels, thereby increasing use efficiency of the radio resources.
To do so, packet service is implemented in many state, depending on channel assignment and the presence or absence of state information. FIG. 6 is a state transition diagram for packet service in a communication system. Referring to FIG. 6, the packet service is comprised of a packet null state, an initialization state, an active state, a control hold state, a suspended state, a dormant state, and a reconnect state. Packet service options are connected in the control hold state, active state, and suspended state.
Upon request for packet service in the packet null state, the initialization state is entered where a connection attempt for packet service is performed, and transition to the control hold state occurs if a dedicated control channel is established. The dedicated control channel is needed to transmit a layer 3 (L3) message and a medium access control (MAC) message. Then, upon entering the active state, forward and reverse dedicated control channels and traffic channels are maintained with RLP (Radio Link Protocol) frames being communicated on these channels. If a relatively short inactive time period is set, the suspended state is entered to efficiently use radio resources and conserve mobile station (MS) power. In the suspended state, the dedicated control and traffic channels are released but can be re-assigned in a relatively short time because both the BS and the MS retain status information including RLP initialization, traffic channel assignment, and encryption variables. If there is no data exchanged for a predetermined time, the suspended state transitions to the dormant state. In the dormant state, only a PPP (Point-to-Point Protocol) connection is maintained and if transmit data is generated, a reconnect state is entered. If the dedicated control channel is established, the reconnect state transitions to the control hold state. While the MS and the BS are in a common channel state, such as the suspended, dormant, and reconnect states, the MS monitors a paging channel and a common control channel on a forward link, and the BS monitors an access channel and a common control channel on a reverse link. There may be a plurality of paging channels and access channels. Each paging channel is distinguished by a different Walsh code and each access channel is distinguished by a different long code.
In FIG. 6, after the active state transitions to the suspended state through the control hold state in the absence of data for a predetermined time during a data communication, messages are exchanged on common channels. Upon generation of a control message for resuming data transmission, the BS attempts to connect to the MS on a paging channel and then the MS transmits a response message on an access channel. However, this common channel message transmission is susceptible to message contention if other MSs use the same access channel, resulting in a reception failure in the BS. If each MS fails to receive an acknowledgement from the BS within a predetermined time, it perceives the occurrence of message contention and resumes a message transmission after a randomized time delay. If repeated attempts to access the access channel for predetermined times fail, the procedure starts again. Information is transmitted on the access channel in access channel slots.
In the mechanism of transmitting an access channel message, the entire process of sending one message and receiving (or failing to receive) an acknowledgement for that message is called an access attempt. Each transmission in the access attempt is called an access probe. Each access probe consists of an access channel preamble and an access channel message capsule. When a message contention occurs, an access probe is re-transmitted with a power level set at a specified amount higher than the previous access probe""s power level after a randomized time delay.
In the case of the MSs initiation of data communication, the same message transmission procedure is performed without the paging step of the BS. If an access channel message is too long to be sent at one time, it is divided into appropriate segments prior to transmission and the above procedure for each segment.
After exchanging the common channel messages, the BS assigns a dedicated code channel and sends a traffic channel assignment message on the dedicated channel. When the BS responds to the message, user data is sent on a dedicated traffic channel.
The procedure of assigning the dedicated channel is implemented in the same manner during transitions from the suspended state to the active state and from the dormant state to the active state. Transition from the suspended state to the active state requires service option negotiation associated with radio resources assignment and RLP initialization because only PPP information is reserved and no radio resources-related information exists in the dormant state.
FIG. 1 describes a conventional data service resuming procedure for a call initiated by a BS in a dormant state. A BS 112 sends a forward control message for resuming a data service to a corresponding addressed MS 114 on a paging channel (F-PCH) being a forward common channel (step 120). Then, the MS 114 sends a response message for the control message on a reverse access channel (R-ACH) (step 122). On the reverse access channel, a preamble precedes an access channel message to facilitate acquisition of a reverse physical channel in the BS 112 (step 126).
The entire process of sending one message and receiving (or failing to receive) an acknowledgement for that message is called an access attempt. Each transmission in the access attempt is called an access probe. Each access probe is comprised of a preamble and a message capsule. Upon contention of access probes, the mobile station transmits an access probe at a progressively higher power level than the previous access probe after a randomized delay. Here, transmission of the preamble is transmitted on a reverse pilot channel to synchronize timing between the BS and the MS which had a communication interrupted.
Reverse access channels share a long code. In a long code sharing scheme, an MS uses a Hash function to determine a long code among all available long codes (access channel long codes) in its initialization state, so that all MSs fairly share the long codes for access channels. A reverse pilot channel for channel estimation is spread by the long code of a reverse access channel and transmitted in parallel with the reverse access channel only for a time period when the reverse channel message exists. The two channels are distinguished by different orthogonal codes.
The preamble is transmitted on the reverse pilot channel at a higher transmit power level than the pilot channel, accompanied by a reverse access channel message. That is, the preamble is a segment of the pilot channel, with a relatively high transmit power.
If the BS 112 succeeds in synchronization with a reverse link and receiving the access channel message (step 126), it sends a dedicated channel assignment message on a forward common control channel (F-CCCH) (step 130) and null traffic on a forward dedicated control channel (F-DCCH) (step 140). If the MS 114 confirms that the dedicated channel is properly assigned from an analysis of the null frame of the F-DCCH, it sends a preamble on its unique code channel (R-PICH) (step 142). The preamble is used to recover synchronization between the BS 112 and the MS 114 which have experienced a temporary call interruption, during the channel assignment.
Then, the BS 112 sends an acknowledgement on the F-DCCH and the MS 114 stops transmitting the preamble (step 150). Thus, the MS 114 is capable of sending a message on a dedicated channel. RLP is initialized for packet data service and service options are connected (step 160). Hence, the control hold state is entered, and if a supplemental channel is successfully assigned (step 170), the active state is entered where packet data is communicated (step 180).
Meanwhile, if the BS 112 initiates a call in the suspended state, the data service can be resumed without step 160 in the above procedure.
FIG. 2 depicts a conventional data service resuming procedure for an MS initiated call in a dormant state. This is the same as the procedure described in FIG. 1 except that the MS 114 sends a packet service origination message on an access channel (step 222). Upon reception of the message by the BS 112, the subsequent steps are performed as shown in FIG. 1.
In resuming a data service for an MS initiated call in a suspended state, step 160 can be omitted in the above procedure.
A conventional data service resuming procedure which exchanges messages on common channels as illustrated in FIGS. 1 and 2, has many disadvantages.
There is a limitation inherent in long code sharing. The equal assignment of available long codes for common channels to mobile stations makes it impossible to control an individual probability of access channel contention for each mobile station. In view of frequent state transitions in the packet data service, the time required for the preliminary process for data transmission including channel acquisition is longer than an actual data transmission time.
Additionally, in a communication on a common channel, the MS must send a message in a slot allocated to the MS, thereby incurring a transmission delay while awaiting the allocated slot.
Also, since a reverse pilot channel is activated only at the time when an access channel message or a reverse common channel message is transmitted, the BS should reacquire the PN sequence of the MS prior to transmission of a channel assignment message. Accordingly, the MS repeatedly performs an access attempt in which a preamble is sent at a relatively high transmit power level, followed by an access channel message. Therefore, power is excessively consumed and the BS reacquisition step is added.
Finally, data can be transmitted only through a regular state transition. In other words, if the amount of data to be transmitted at a time is small, the resources that a preliminary process for resuming data transmission takes is larger than that of actual data transmission, leading to inefficient use of resources.
In a conventional designation of a common channel, an MS transmits a message on a reverse access channel and receives a response for the message on a forward paging channel. Thus, there may exist a plurality of forward paging channels and reverse access channels. Each forward channel is distinguished by a different Walsh code and each reverse channel by a different long code in a CDMA mobile communication system.
Upon generation of a message to be transmitted, the MS sends the message together with a preamble to the BS on an available access channel at an appropriate power level, and awaits an acknowledgement from the BS. If a different MS selects the same access channel, message contention occurs. Then, the BS may fail to receive the MS initiated message for a predetermined time. If it does, the MS sends the same message again using a power level set at a specified amount higher than the previous message and awaits an acknowledgement.
In the conventional mechanism of sending access channels being reverse common channels, concurrent message transmissions from MSs with the same long code are likely to cause message contention, leading to message losses. This is called contention-based random access.
When message contention occurs, the MS perceives the message contention in a predetermined time and resumes a message transmission after a randomized time delay. The MS performs an initial attempt to access the BS at a predetermined power level. When it fails to receive an acknowledgement from the BS, it performs the next attempt using a power level set at a specified amount higher than the previous attempt. If repeated attempts to access the access channel for predetermined times fail, the procedure starts again. Information is transmitted on the access channel in access channel slots and access channel frames.
For an MS to transmit a message which is too long to be transmitted at one time, the message must be divided into appropriate segments which are sent a plurality of times. When other MSs attempt to transmit messages using the same long code, message contention occurs. In this case, a long delay is involved in transmitting the entire message on the access channel.
The message contention can be prevented by designating a channel assigned by a BS as dedicated to an MS for transmission of a common channel message. On the other hand, to designate a forward common channel as dedicated, the MS requests for channel continuously transmit a common channel message, and then the BS sends a response message which includes the ID of an available channel.
The present invention provides a method of transitioning from a dedicated channel released state to a data transmission state by rapidly assigning a dedicated channel.
An object of the present invention is to provide device and method for communicating packet data, in which data transmission on a common channel is minimized and a data transmission state using a dedicated channel, or a channel designated as dedicated, is rapidly entered in order to efficiently use resources and support rapid data service.
According to one aspect of the present invention, the above object can be achieved by providing a BS transmitting device in a mobile communication system. In the transmitting device, a data generator generates frame data to be transmitted, a first mask generator generates a long code generator for a forward common channel, a second mask generator generates a long code mask for a forward common channel to be designated as dedicated to a specific mobile station, a selector selects one of the long code masks generated in the first and second mask generators, a long code generator generates a long code by use of the selected long code mask, a scrambler mixes the frame data received from the data generator and the long code received from the long code generator, and a transmitter spreads the scrambled frame, for transmission.